Preeclampsia, a pregnancy-related endothelial disorder, is associated with both cardiovascular and cerebrovascular complications. Preeclampsia requires the presence of a placenta as part of its pathophysiology, yet the role of this organ in the cerebrovascular complications remains unclear. Research has shown that circulating small extracellular vesicles (also known as exosomes) present in preeclampsia plasma can generate endothelial dysfunction, but it is unclear whether the impairment of function of brain endothelial cells at the blood-brain barrier is secondary to plasma-derived or placental-derived exosomes. In this study, we evaluated the effect of small extracellular vesicles isolated from plasma samples of women with preeclampsia (n=12) and women with normal pregnancy (n=11) as well as from human placental explants from normotensive pregnancies (n=6) subjected to hypoxia (1% oxygen) on the integrity of the blood-brain barrier, using both in vitro and animal models. Exposure of human-derived brain endothelial cell monolayers to plasma and plasma-derived small extracellular vesicles from preeclamptic pregnancies increased the permeability and reduced the transendothelial electrical resistance. A similar outcome was observed with hypoxic placental-derived small extracellular vesicles, which also increased the permeability to Evan’s blue in the brain of C57BL6 nonpregnant mice. Cotreatment with magnesium sulfate reversed the effects elicited by plasma, plasma-derived, and hypoxic placental-derived small extracellular vesicles in the employed models. Thus, circulating small extracellular vesicles in plasma from women with preeclampsia or from hypoxic placentae disrupt the blood-brain barrier, which can be prevented using magnesium sulfate. These findings provide new insights into the pathophysiology of cerebral complications associated with preeclampsia.